Abstract:

Homobimetallic dicobalt complexes featuring vastly different coordination environments have been synthesized, and their multielectron redox chemistry has been investigated. Treatment of CoX2 with K[MesNPiPr2] leads to self-assembly of [(THF)Co(MesNPiPr2)2(μ-X)CoX] [X = Cl (1), I (2)], with one Co center bound to two amide donors and the other bound to two phosphine donors. Upon two-electron reduction, a ligand rearrangement occurs to generate the symmetric species (PMe3)Co(MesNPiPr2)2Co(PMe3) (3), where each Co has an identical mixed P/N donor set. One-electron oxidation of 3 to generate a mixed valence species promotes a ligand rearrangement back to an asymmetric configuration in [(THF)Co(MesNPiPr2)2Co(PMe3)][PF6] (4). To construct rigid bimetallic cobalt complexes, a series of triply bridged phosphinoamide complexes been synthesized. Reaction of K[MesNPiPr2] with CoCl2 in THF results in the formation of a brown crystalline solid, Co(µ-iPrNPPh2)3Co(η2-iPrNPPh2) (6). The one electron bulk chemical reduction in the absence and presence of two-electron σ-donor ligands yields Co(µ-iPrNPPh2)3Co(iPrNHPPh2) (7) and Co(µ-iPrNPPh2)3Co(PMe3) (8). Treatment of 8 with organic azides results in the formation of two-electron oxidized Co(µ-iPrNPPh2)3Co≡NMes (9, Mes = 2,4,6-trimethylphenyl). In contrast to 9, the reaction of 8 with Ph2CN2 led to the formation of unexpected two-electron phosphine oxidized product [Co(µ-iPrNPPh2)2(µ-iPrNPPh2N2CPh2)Co] (11). Ligand substitution reactions of 8 with Et4N-N3 and KOH resulted to the formation of [Co(µ-iPrNPPh2)3Co(N3)][Et4N] (12) and [Co(µ-iPrNPPh2)3Co(OH)](KC12H24O6) (13), respectively.